Analysis of the imaging principle of virtual reality glasses (augmented reality glasses)

First of all, this article only introduces the existing common "helmet + lens + screen" imaging principle, other (such as light field imaging, etc.) temporarily do not parse, look forward to the next update ~

If you understand the principle of magnifying glass, I think the principle of the glasses you are not difficult to understand.

Virtual reality glasses are now generally the structure of "lens + screen" imaging mode, the lens in front of the 2-3cm, screen distance lens 3-6cm, virtual image imaging in front 25cm-50cm around. (This brings the problem of vision fatigue, when wearing helmet glasses, the line of sight will continue to focus on the 25cm-50cm, unable to move, and the field of vision is all electronic display, the eye muscles will be extremely tired after a long time, imagine your eyes from the TV screen half a meter is not moving ... But the above-mentioned light field imaging is to imitate the real world real light field information, eye focus Point will continue to move, without the above problems)

1, magnifying glass imaging principle

When the object AB is placed outside the lens focal length F, an inverted magnification real image a′b′ (1-1 (A)) is obtained, and its position is twice times the focal length. If you place the object AB in the lens focal length, you can see a magnified virtual image a′b′ (1-1 (B)). The ratio of the length of the image to the length of the object (A′B′/AB) is the magnification of the magnifying glass (magnification). If the distance between the magnifying glass and the object is approximately equal to the focal length of the lens (A≈F), and the distance between the magnifying glass and the image is approximately equal to the apparent distance of the human eye (250mm), the magnification of the magnifying glass is: n=b/a

[Ps: The human eye can see the object's nearest distance is called the apparent distance. In fact, the apparent distance varies from person to person, for myopia, the apparent distance will be shorter, farsighted eyes longer. For healthy human eyes, the apparent distance is around 250mm, so we usually set the apparent distance to 250mm. ］

It is known that the shorter the focal length of the lens, the larger the magnification of the magnifying glass. generally used magnifying glass focal length within the 10~100mm range, and thus magnification in the 2.5~25 times . further high magnification will blur the resulting image due to the shortening of the lens focal length and the excessive increase of surface curvature. In order to get a higher magnification, a microscope is used, allowing the magnification to reach 1500~2000 times.

In magnifying glass imaging, the object distance a (u in the equation diagram), the image distance B (v in the equation diagram), the focal length F conforms to the following relationship

namely 1/b+1/a=1/f

Because like virtual image, B will be negative here;

2. Imaging principle of head-wearing glasses

For example, according to the above content, the focal length needs to be larger than the material distance, and the general optical object distance in 5-7cm, we set the lens focal length f is 70mm, set the screen object distance A is 55mm, according to the formula of the b=-1/(1/f-1/a) =256.6mm, just is the apparent distance around. And because the existing glasses generally can not adjust the screen distance, so a basic fixed, can change the lens to adjust F to achieve virtual image distance transformation, for myopia, the image distance needs to be shorter, F needs to increase, generally choose thinner lens, for hyperopia choose thicker lens. In addition, in the adjustment of several parameters, the basic is a few millimeters of fine-tuning, it is necessary to weigh the virtual image distance too large (large magnification) and the pixel particles caused by the problem and virtual image distance too close to bring the lack of apparent distance, small field of view and so on.

So at this point, you will understand the passage at the beginning of the article:

Wearing helmet glasses, the line of sight will continue to focus on the 25cm-50cm, can not be moved, and the field of vision is all electronic display, long after the eye muscles will be extremely tired, imagine your eyes from the TV screen half a meter is not moving ...

The article is relatively hasty, welcome to the Ming Exchange, thank you!

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In addition, optical field imaging my understanding is that the device directly to the glasses projection (through the lens array or other technology) of the real light field information, the light field information you can understand the real world is full of light collection, the human eye is also through the lens focal length of the transformation of different beams focused on the retina, But in fact, the light field in the eyes of the information has not changed, is holographic, but the human eye with focus on the selection.

Analysis of the imaging principle of virtual reality glasses (augmented reality glasses)